Under-staffing was partly to blame for a spate of recent blunders by the Immigration Department, its deputy chief said on the eve of his retirement.
Deputy Director of Immigration Choy Ping-tai said the manpower shortage was the biggest challenge facing the body.
It was like an over-stretched rubber band that could snap at any moment, he said.
The department has come under criticism for various errors, including the chopping of incorrect dates on travellers' documents.
In one case, a two-way permit holder was given a seven-year stay instead of three months.
'We handle 13 million cases a year and most of the cases involved chops,' Mr Choy said. 'But there are just a few cases involving wrongly chopped dates.
'We're ready to admit mistakes. Sometimes mistakes resulted from busy workloads.
'The officers involved would be disciplined, but we'd also have to review if we've put 'too much straw on their backs'. I made mistakes too when I was a junior officer because of the workload.'
Among the most serious blunders was immigration officers sending autistic boy Yu Man-hon across the border to Shenzhen in August.
The 15-year-old missing boy's parents have sued for negligence.
Mr Choy retires tomorrow. He turns 55 on Friday, having spent 34 years with the department.
He said the department had not seen any manpower increase to cope with an expanding workload, especially at the Lowu border checkpoint where the number of commuters was increasing by 15 to 17 per cent a year.
He said the 'last straw' regarding the manpower shortage was not far away.
The department is seeking to add 117 officers to the Lowu checkpoint, currently manned by 500 officers.
It is also seeking extra security officers at Immigration Tower in Wan Chai, which has been strengthened following the fatal arson attack in August which killed senior immigration officer Leung Kam-kwong and abode seeker Lam Siu-sing.
Mr Choy said he foresaw the department changing in two main ways: development of information technology, and a cultural change to strengthen care and respect for the people the department served.
He said he had no plans to take up other jobs after retirement and would make up for lost time with his two sons.